None of us need reminding that the American (in particular) and Global economies are rather unstable at present. The man on the street knows it as well, and that's more of a problem than the actual economic difficulties.
Whilst we have upbeat predictions about online ad-spend remaining high, that didn't happen in the previous mini-burst. Advertising cuts killed Gen I at the end of the day to the extent that many big names died out or were unable to sustain their bloated infrastructures.
You have to look at the bigger picture; with tightening belts cable TV will go first, with the internet and online shopping, long before the car which enables offline shopping.
Offline advertising contracts are generally contracts and signed up for long periods and in advance with agencies and prebooked in media. They can't be cut quick, but online advertising spends can.
Once the online ads get cut as a quick cashflow fix, the company isn't then going to terminate offline ads and reintroduce online ads due to slightly better performance due to the risk associated and the money invested in offline campaigns.
A large chunk of e-commerce still caters for the non-necessity market. Far more is spent on MP3 players and the like online than is spent on bread, rice and potatoes. This too means that all belt-tightening has a disproportionate effect online.
Companies know that whatever happens, if they can keep their product on the highstreets then 99% of their customers can get there and buy. That's an assurance that the internet cannot give in a worst come to the worst situation.